The present proprietor has developed open filters named "AQUAZUR", which are described in particular in the "Memento Technique de l'Eau" (Technical Review of Water)--page 772-783--Vol. 2--9th Edition--published by the company DEGREMONT--1989--(Editions Lavoisier) to which the reader may refer.
This type of filtering device comprises an open tank made of concrete, comprising a floor which is also generally made of concrete and fitted with nozzles, on which the bed of filtering material is arranged, untreated water being supplied via supply channels arranged laterally along the tank, the filtered water being removed below the floor via an axial, longitudinal conduit. In this type of known filter, the particles of the filtering bed are washed by admitting washing water and air below the floor possessing nozzles, the washing waters being removed via a longitudinal channel arranged along the axis of the tank.